Hi Dru, What do you mean by "synthetic" here ?
Technically, "Synthetic" means a language with a "high morpheme-per-word ratio". More generally, it describes a language like Latin where syntax expresses itself by inflecting the word itself, rather than using more words to do this, e.g. amo, amas, amat, English I love, thou lovest, he/she/it loves. In Latin the, o, as and at endings replace, I, thou, he/she/it. Latin is more synthetic than English, but the est and s in that sequence in English are synthetic. The opposite of 'synthetic' is 'analytic'. Very few languages are wholly one or the other.
In Latin, the more complex tenses are often formed by yet more changes to the verb, rather than constructions using auxiliaries as in English. Likewise nouns change their endings in circumstances where in English we'd use a preposition.
Greek and Hebrew are both more synthetic than English, though English is more synthetic than we sometimes realise. in addition to the example above, take another word from the previous paragraph, 'constructions'. The s inflection makes it plural. The ion inflection makes it a noun.
As a digression, although construct is usually a verb, it exists as a noun with a different meaning from construction. But, and this is feature which is widespread in English but may be linguistically slightly unusual, the stress pattern changes. As a verb, the stress falls on the second syllable. As a noun it falls on the first. There are a number of examples of single syllable words where the weight shifts in a similar way, e.g. calf, calve.