"This is a big spider!"
Translation:To duży pająk!
Is the phrase "To duży pająk" really equivelent to "To jest duży pająk"?
It seems the former simply refers to the big spider whereas the latter describes something AS a big spider.
Are these simply interchangeable in spoken Polish, or is the meaning inferred from context?
It is equivalent. "To jest" is often shortened just to "To". "To" is the subject here, and doesn't depend on the gender. So both mean "This is a big spider"
"Ten duży pająk" would be "this big spider".
It could be ambiguous with neuter nouns, as then 'to' could be either the subject, or a neuter pronoun, so theoretically "To duże drzewo" could be both "This is a big tree" and "this big tree". However, if it ends with a dot, than as a sentence it can only mean "This is a big tree".
Don't worry, you'll get it :) So basically yes, "ten" is a masculine pronoun meaning "this", and pająk is indeed masculine. It would be used if you were to translate a sentence "This spider is big": Ten pająk jest duży.
But here we have a sentence of the "This is Y" type. And in such a sentence, no matter the gender or the number, whether we will have this/that/these/those in the English sentence, in Polish it will always be "To".
P.S. If you are by any chance an English native, you can just change your keyboard to a Polish one, you will have all that you need for English plus all you need for Polish :)