early 15c. (implied in deteined), "keep back or away, withhold," from Old French detenir "to hold off, keep back" (12c.), from Latin detinere "hold off, keep back," from de "from, away" (see de-) + tenere "to hold" (from PIE root *ten- "to stretch").
Legal sense of "to hold in custody" is from late 15c. (late 13c. in Anglo-French). Meaning "keep or restrain from proceeding" is from 1590s. Modern spelling is 17c., from influence of contain, retain, etc. Related: Detained; detaining.
1580s, "to watch, guard, or keep order; to govern," from French policer, from police (see police (n.)). The original sense is obsolete. The meaning "to control or keep order in by means of police" is from 1837; figurative use by 1885. Related: Policed; policing.
c. 1300, maintenen, "to support, uphold, aid;" also "hold fast, keep in possession, preserve from capture or loss," from Anglo-French meintenir (Old French maintenir, 12c.) "keep (a wife), sustain; persevere in, practice continually," from Latin manu tenere "hold in the hand," from manu, ablative of manus "hand" (from PIE root *man- (2) "hand") + tenere "to hold" (from PIE root *ten- "to stretch").
Sense of "hold in an existing state or condition, keep in existence or continuance" is from early 14c. Meaning "to carry on, keep up" is from mid-14c.; that of "to keep oneself, support" is from late 14c. Sense of "defend in speech, uphold by argument or assertion" is from mid-14c. Meaning "practice habitually" is from c. 1400. Sense of "furnish means for the subsistence or existence of" is from c. 1400. Related: Maintained; maintaining; maintains.
"to guard, protect, keep secure from danger," mid-15c., from safeguard (n.). Related: Safeguarded; safeguarding.
Old English bihaldan (West Saxon behealdan) "give regard to, hold in view," also "keep hold of; belong to," from be- + haldan, healdan (see hold (v.)). Related: Beheld; beholding. A common West Germanic compound, compare Old Saxon bihaldan "hold, keep," Old Frisian bihalda "hold, possess, keep, protect, save," Old High German bihaltan, German behalten, but "[t]he application to watching, looking, is confined to English" [OED]. Related: Beholding.