go at it

Etymology
or

Verb

 * I can't figure out this problem. I've been going at it [going at the problem] for hours now.
 * 1)  To engage in some activity, especially vigorously or enthusiastically.
 * We were all going at it like crazy, trying to get the job finished before the deadline.
 * 1)  To fight.
 * 2)  To have sex.
 * 1)  To fight.
 * 2)  To have sex.
 * 1)  To have sex.
 * 1)  To have sex.