At will

the faculty of conscious and especially of deliberate action; the power of control the mind has over its own actions:
the freedom of the will.
power of choosing one’s own actions:
to have a strong or a weak will.
the act or process of using or asserting one’s choice; volition:
My hands are obedient to my will.
wish or desire:
to submit against one’s will.
purpose or determination, often hearty or stubborn determination; willfulness:
to have the will to succeed.
the wish or purpose as carried out, or to be carried out:
to work one’s will.
disposition, whether good or ill, toward another.
Law.

a legal declaration of a person’s wishes as to the disposition of his or her property or estate after death, usually written and signed by the testator and attested by witnesses.
the document containing such a declaration.

to decide, bring about, or attempt to effect or bring about by an act of the will:
He can walk if he wills it.
to purpose, determine on, or elect, by an act of will:
If he wills success, he can find it.
to give or dispose of (property) by a will or testament; bequeath or devise.
to influence by exerting control over someone’s impulses and actions:
She was willed to walk the tightrope by the hypnotist.
to exercise the will:
To will is not enough, one must do.
to decide or determine:
Others debate, but the king wills.
at will,

at one’s discretion or pleasure; as one desires:
to wander at will through the countryside.
at one’s disposal or command.

verb (past) would takes an infinitive without to or an implied infinitive
esp with you, he, she, it, they, or a noun as subject. used as an auxiliary to make the future tense Compare shall (sense 1)
used as an auxiliary to express resolution on the part of the speaker: I will buy that radio if it’s the last thing I do
used as an auxiliary to indicate willingness or desire: will you help me with this problem?
used as an auxiliary to express compulsion, as in commands: you will report your findings to me tomorrow
used as an auxiliary to express capacity or ability: this rope will support a load
used as an auxiliary to express probability or expectation on the part of the speaker: that will be Jim telephoning
used as an auxiliary to express customary practice or inevitability: boys will be boys
(with the infinitive always implied) used as an auxiliary to express desire: usually in polite requests: stay if you will
what you will, whatever you like
(informal) will do, a declaration of willingness to do what is requested
noun
the faculty of conscious and deliberate choice of action; volition related adjectives voluntary volitive
the act or an instance of asserting a choice

the declaration of a person’s wishes regarding the disposal of his or her property after death related adjective testamentary
a revocable instrument by which such wishes are expressed

anything decided upon or chosen, esp by a person in authority; desire; wish
determined intention: where there’s a will there’s a way
disposition or attitude towards others: he bears you no ill will
at will, at one’s own desire, inclination, or choice
with a will, heartily; energetically
with the best will in the world, even with the best of intentions
verb (mainly transitive; often takes a clause as object or an infinitive)
(also intransitive) to exercise the faculty of volition in an attempt to accomplish (something): he willed his wife’s recovery from her illness
to give (property) by will to a person, society, etc: he willed his art collection to the nation
(also intransitive) to order or decree: the king wills that you shall die
to choose or prefer: wander where you will
to yearn for or desire: to will that one’s friends be happy
v.

Old English *willan, wyllan “to wish, desire, want” (past tense wolde), from Proto-Germanic *welljan (cf. Old Saxon willian, Old Norse vilja, Old Frisian willa, Dutch willen, Old High German wellan, German wollen, Gothic wiljan “to will, wish, desire,” Gothic waljan “to choose”). The Germanic words are from PIE *wel-/*wol- “be pleasing” (cf. Sanskrit vrnoti “chooses, prefers,” varyah “to be chosen, eligible, excellent,” varanam “choosing;” Avestan verenav- “to wish, will, choose;” Greek elpis “hope;” Latin volo, velle “to wish, will, desire;” Old Church Slavonic voljo, voliti “to will,” veljo, veleti “to command;” Lithuanian velyti “to wish, favor,” pa-vel-mi “I will,” viliuos “I hope;” Welsh gwell “better”).

Cf. also Old English wel “well,” literally “according to one’s wish;” wela “well-being, riches.” The use as a future auxiliary was already developing in Old English. The implication of intention or volition distinguishes it from shall, which expresses or implies obligation or necessity. Contracted forms, especially after pronouns, began to appear 16c., as in sheele for “she will.” The form with an apostrophe is from 17c.
n.

Old English will, willa, from Proto-Germanic *weljon (cf. Old Saxon willio, Old Norse vili, Old Frisian willa, Dutch wil, Old High German willio, German wille, Gothic wilja “will”), related to *willan “to wish” (see will (v.)). The meaning “written document expressing a person’s wishes about disposition of property after death” is first recorded late 14c.
Freely, as one pleases, as in The grounds are open to the public and one can wander about at will, or With this thermostat you can adjust the room temperature at will. [ 1300s ]
In addition to the idiom beginning with
will
also see:

against one’s will
at will
boys will be boys
heads (will) roll
murder will out
of one’s own accord (free will)
shit will hit the fan
that will do
time will tell
truth will out
when the cat’s away, mice will play
where there’s a will
with a will
with the best will in the world
wonders will never cease