Here are some possibilities:
* "acro-": This prefix means "height", "summit", or "peak". Examples include "acrobat" (one who performs high feats), "acropolis" (a high city), and "acromegaly" (a condition causing abnormal growth of the extremities).
* "acr-": This could be a misremembered form of "acro-".
* "a-cr-": This might be a compound prefix, with "a-" meaning "without" or "not" and "cr-" potentially stemming from another root word.
If you provide more context about the word containing the prefix "acr", I can give you a more specific answer.