coltach most certainly doesn not mean weather; it’s an adjective meaning similar, (a)like, especially with the preposition ri, eg. coltach ris an fhear sin similar to that man, like that man
The words for weather in Gaelic are sìde and aimsir (this one also means time), both feminine nouns.
You might have seen it in a sentence like cò ris a tha an t-sìde coltach? what is the weather like?, more lit: what to is it that the weather is similar?
You could have seen coltach in one of those exercises: