All answer words must be entries in the latest edition of the Concise Oxford English Dictionary (COED). The 11th edition was published in 2004 and new editions appear approximately every five years.
Answer words must be listed in COED without capital letters. For example, “Moonie” and “Miocene” aren’t allowed.
Answers must be listed in COED as single words, without hyphens or other punctuation such as apostrophes. For example, “come on” and “come-on” aren’t allowed.
Plural nouns aren’t allowed, even if they’re irregularly formed. For example, “coins”, “monies” and “icemen” aren’t allowed. Neither are words like “folk” which COED lists only as a plural noun. However, if a plural form is explicitly listed in COED as a different part of speech, it is allowed. For example, “bats” (adjective), “lots” (adverb) and “times” (verb meaning “to multiply”) are allowed.
Only the base forms of verbs are allowed (the infinitive, without the word “to”), not any variations such as present tense, past tense or participles, even if they’re irregularly formed. For example, “see” is allowed, but not “sees” or “seen”. However, if a verb form is explicitly listed in COED as a different part of speech, it is allowed. For example, “saw” (noun), “seeing” (conjunction or noun) and “given” (adjective, preposition or noun) are allowed.
Agent nouns ending in -er are allowed if they’re listed in COED. For example, “mincer” is allowed, but “mooner” isn’t.
Basic forms of adjectives are allowed, but not comparatives (usually ending in -er) or superlatives (usually ending in -est). For example, “nice” is allowed, but “nicer” and “nicest” aren’t. Irregular comparatives and superlatives such as “better”, “best” and “worse” are disallowed as forms of adjectives, but many of them are also listed in COED as other parts of speech (eg “worst” = “get the better of”), and are therefore allowed on that basis.
Adverbs ending in -ly aren’t allowed.
Any word in COED is allowed, even if it’s marked as slang, archaic, US, etc.
The minimum word length varies through the week.
On Mondays and Tuesdays the Polygon has a total of seven letters, and answer words must be at least three letters in length. The total number of letters is eight on Wednesdays and Thursdays, nine on Fridays and ten on Saturdays, and answers must be at least four letters long on those days.