Is there a word that if I read letters a, b, c from the crossword puzzle and make a word abc the what have I done to those letters? I was thinking that I catenate or concatenate letters but I was said that is wrong in a comment to this post on Puzzling SE: Proving the existence of a given matrix. Is the proper word to join letters to make a word?
Concatenate is correct.
verb (used with object), concatenated, concatenating.
1. to link together; unite in a series or chain.
You could also say put together.
phrasal verb [transitive]
to make something by joining all its parts
- I concatenate a, b, c to make abc.
- I put together a, b, c to make abc.
Concatenate sounds formal, and it especially sounds like programming jargon to me. Put together sounds simple. You could also try link, join, and connect.
By the way, the user was not complaining that concatenate was incorrect.
Excerpt from revision history number 1 of the linked OP:
Prove that there is a 9x13 matrix containing the digits such that one can read the squares of 1,...,100. Here read means that you fix the starting position and direction (8 possibilities) and then go to that direction by catenating the numbers.
[...] (4) even if you mean “concatenate”, the sentence “go to that direction by concatenating the numbers.” doesn’t make sense.[...] – Peregrine Rook
He/she was complaining that the sentence didn't make sense. It makes sense to concatenate 1, 2, 3 (= 123), but it does not make sense to concatenate and "go to that direction". Also, idiomatically, it should be (and was corrected to) "go in that direction", but it still doesn't make sense. I think you meant something like ... and then concatenate the digits (found) along that path/direction.