言い難い (iigatai: difficult to say, inexpressible) to say + difficult
Even though we most often see 難 with the yomi of muzuka(shii) or NAN, it can also have the kun-yomi of kata(i). This is somewhat confusing if we typically think of kata(i) as 固 (stiff, hard, firm, solid), 堅 (firm, solid, hard), or 硬 (hard). All these tributaries must have flowed from the same river at one point. That is, I suspect that katai originally meant all these things, with the Japanese later assigning different kanji to the various shadings of katai to draw slight distinctions.
