lend a hand

Old English hond, hand "hand; side; power, control, possession," from Proto-Germanic *khanduz (cf. Old Saxon, Old Frisian, Dutch, German hand, Old Norse hönd, Gothic handus). The original Old English plural handa was superseded in Middle English by handen, later hands.

Meaning "person who does something with his hands" is from 1580s, hence "hired workman" (1630s) and "sailor in a ship's crew" (1660s). Clock and watch sense is from 1570s. Meaning "round of applause" is from 1838. The linear measure of 4 inches (originally 3) is from 1560s, now used only in giving the height of horses. The meaning "playing cards held in one player's hand" is from 1620s; that of "a round at a card game" is from 1620s.

First hand, second hand, etc. (mid-15c.) are from the notion of something being passed down from hand to hand. Out of hand (1590s) is opposite of in hand "under control" (c.1200). Hand over fist (1825) is suggestive of sailors and fishermen hauling in nets. Hand jive is from 1958. To win something hands down (1855) is from horse racing, from a jockey's gesture of letting the reins go loose in an easy victory.

To hand it to (someone) "acknowledge someone's ability" is slang from c.1906. Phrase on the one hand ... on the other hand is recorded from 1630s, a figurative use of the physical sense of hand in reference to position on one side or the other side of the body (as in the lefthand side), which goes back to Old English Hands up! as a command from a policeman, robber, etc., is from 1873. Hand-to-mouth is from c.1500. Hand-in-hand attested from c.1500 as "with hands clasped;" figurative sense of "concurrently" recorded from 1570s.