Wiktionary
vb. 1 (context intransitive English) To form a small group. 2 (context intransitive English) to become friends with.
WordNet
Usage examples of "pal up".
He was a chap who seemed ready to pal up with any one, and I could not but recall the strange assertion I had so often heard that in America one never knows who is one's superior.
And so they go on, some nice and some nasty, and some bright and some dull, but they pair off and pal up more or less, and finally comes the afterthought which like the first-born gets an undue share of attention.
We'll go and find out who he is, and pal up with him, and maybe he'll take us out fishing in the boat, said Philip at once.
Well, in the meanwhile, of course, he is entertained and may pal up with anyone or get himself into Lord knows what.
But to take me into his home-- pal up with me--when there was any kind of a chance that I might mean trouble.