>I always thought ligature was the printers word, and digraph was the language term.

not unexpectedly, the meanings have become smushed (at least in the U.S.) - the newest sense of digraph is ligature. I think that shanks was looking for the word that applies to printing (shanks?) which would be ligature and
sometimes digraph.

Main Entry: di·graph
Pronunciation: 'dI-"graf
Function: noun
Date: 1780
1 : a group of two successive letters whose phonetic value is a single
sound (as ea in bread or ng in sing) or whose value is not the sum of a
value borne by each in other occurrences (as ch in chin where the
value is \t\ + \sh\)
2 : a group of two successive letters
3 : LIGATURE 4

p.s. - shanks, your bet may require a recount; I was thinking it was either dieresis or digraph, the latter leading of course to the more accurate ligature... but the oddest thing (to me, at least) is that the original spelling of dieresis (and still the Brit spelling?) was diaeresis, with the ć ligature.