Syntaxes

3 clues
Grammatical rules
Sentence structures
Grammarians' subjects
Similar answers:
Aaltosaxes
Additionaltaxes
Aftertaxes
Airwaxes
Altosaxes
Andtaxes
Anticlimaxes
Axes
Axeseightandup
Backtaxes
Baritonesaxes
Beertaxes
Beforetaxes
Bettermenttaxes
Broadaxes
Carwaxes
Catononestaxes
Climaxes
Climaxesat
Coaxes