1 tr. perceive the meaning of (words, a person, a language, etc.) (does not understand what you say; understood you perfectly; cannot understand French).
2 tr. perceive the significance or explanation or cause of (do not understand why he came; could not understand what the noise was about; do not understand the point of his remark).
3 tr. be sympathetically aware of the character or nature of, know how to deal with (quite understand your difficulty; cannot understand him at all; could never understand algebra).
4 tr. a (often foll. by that + clause) infer esp. from information received, take as implied, take for granted (I understand that it begins at noon; I understand him to be a distant relation; am I to understand that you refuse?). b (absol.) believe or assume from knowledge or inference (he is coming tomorrow, I understand).
5 tr. supply (a word) mentally (the verb may be either expressed or understood).
6 intr. have understanding (in general or in particular).
Phrases and idioms:
understand each other
1 know each other's views or feelings.
2 be in agreement or collusion.
Derivatives:
understandable adj. understandably adv. understander n.
Etymology: OE understandan (as UNDER-, STAND)
Useful english dictionary. 2012.