At length

the longest extent of anything as measured from end to end:
the length of a river.
the measure of the greatest dimension of a plane or solid figure.
extent from beginning to end of a series, enumeration, account, book, etc.:
a report running 300 pages in length.
extent in time; duration:
the length of a battle.
a distance determined by the extent of something specified:
hold the picture at arm’s length.
a piece or portion of a certain or a known extent:
a length of rope.
the quality or state of being long rather than short:
a journey remarkable for its length.
the extent to which a person might or would go in pursuing something:
he went to great lengths to get what he wanted.
a large extent or expanse of something.
the measure from end to end of a horse, boat, etc., as a unit of distance in racing:
the horse won by two lengths.
clothing. the extent of a garment related to a point it reaches, as on the wearer’s body, the floor, or on a garment used as a standard of measurement (usually used in combination):
an ankle-length gown; a floor-length negligee; a three-quarter-length coat.
prosody, phonetics.

(of a vowel or syllable) quant-ty, whether or short.
the quality of vowels.

bridge. the possession of four or more than four cards in a given suit.
theater archaic. 42 lines of an acting part.
at length,

in or to the full extent; completely.
after a time; finally:
at length there was a step forward in the negotiations.

go to any length / lengths, to disregard any impediment that could prevent one from accomplishing one’s purpose:
he would go to any lengths to get his own way.
keep at arm’s length. 1 (def 16).
noun
the linear extent or measurement of something from end to end, usually being the longest dimension or, for something fixed, the longest horizontal dimension
the extent of something from beginning to end, measured in some more or less regular units or intervals: the book was 600 pages in length
a specified distance, esp between two positions or locations: the length of a race
a period of time, as between specified limits or moments
something of a specified, average, or known size or extent measured in one dimension, often used as a unit of measurement: a length of cloth
a piece or section of something narrow and long: a length of tubing
the quality, state, or fact of being long rather than short
(usually pl) the amount of trouble taken in pursuing or achieving something (esp in the phrase to great lengths)
(often pl) the extreme or limit of action (in phrases such as to any length(s), to what length(s) would someone go, etc)
(prosody, phonetics) the metrical quant-ty or temporal duration of a vowel or syllable
the distance from one end of a rectangular swimming bath to the other compare width (sense 4)
(prosody) the quality of a vowel, whether stressed or unstressed, that distinguishes it from another vowel of similar articulatory characteristics. thus (iː) in english beat is of greater length than (ɪ) in english bit
(cricket) the distance from the batsman at which the ball pitches
(bridge) a holding of four or more cards in a suit
(nz, informal) the general idea; the main purpose
at length

in depth; fully
eventually
for a long time; interminably

n.

old english lengðu “length,” from proto-germanic -langitho, noun of quality from -langgaz (root of old english lang; see long) + –itho, abstract noun suffix (see -th (2)).

cognate with old norse lengd, old frisian lengethe, dutch lengte. figurative sense of “the distance one goes, extremity to which something is carried” is from 1690s. phrase at length “to full extent” is attested from c.1500.

length (lěngkth, lěngth)
n.
the linear distance between two points.

noun

female s-xual gratification (1968+)
in full, extensively. for example, the preacher went on at length about sin, or i have read at length about these cameras. [ c. 1500 ]
after a long time, finally, as in at length the procession ended. [ early 1500s ]
also see: in the long run
see:

at arm’s length
at length
go to any length