constrain v.

word-forming element meaning "together, with," sometimes merely intensive; it is the form of com- used in Latin before consonants except -b-, -p-, -l-, -m-, or -r-. In native English formations (such as costar), co- tends to be used where Latin would use con-.

c. 1300, "tie, bind, fasten, gird," from present participle stem of Old French estreindre "bind tightly, clasp, squeeze," from Latin stringere (2) "draw tight, bind tight, compress, press together," from PIE root *streig- "to stroke, rub, press" (source also of Lithuanian strėgti "congeal, freeze, become stiff;" Greek strangein "twist;" Old High German strician "mends nets;" Old English streccian "to stretch;" German stramm, Dutch stram "stiff").

From late 14c. as "tighten; make taut," also "exert oneself; overexert (a body part)," Sense of "press through a filter, put (a liquid) through a strainer" is from early 14c. (implied in strainer); that of "to stress beyond measure, carry too far, make a forced interpretation of" is from mid-15c. Related: Strained; straining.