Per Should we prefer plural in tags?, for consistency with EL&U and other StackExchange sites, I believe the consensus was to use plural tag names for countables. In practice, we have something of a mishmash of singular and plural forms, particularly for terminology related to punctuation, sentence components, word forms, and parts of speech. In fact, we have both part-of-speech (21 questions) and parts-of-speech (6).
I propose we make parts-of-speech the canonical tag, and that we pluralize the following:
For the others, I ask only that we choose a consistently singular or plural form.
Parts of speech
Phrases and clauses
- parenthesis (yes, I checked, they're about parentheses, not parenthesis, unlike the better-curated ellipsis)