In the dictionary, when you’re looking up a noun that ends in s, you’re apt to find a notation like this: “noun plural but singular in construction.” What does that mean?
This description refers to words like news that appear to be plural but take a singular verb (hence the word construction, meaning “sentence structure,” not “appearance”). One category of words plural in appearance but singular in use is that of intellectual pursuits and their associated academic disciplines: For mathematics, physics, and the like, we use a singular verb: “Mathematics is difficult for him”; “The physics is staggeringly complex.” However, similar terms may use singular or plural verbs depending on the sense: “Statistics is not my favorite subject”; “The statistics are valid.”
In other contexts, usage varies. Gymnastics is treated singularly (“Gymnastics is an Olympic sport”), but calisthenics takes a plural verb (“Calisthenics are boring”). Both words refer to a routine of physical activities, but noun-verb agreement is inconsistent.
Some words that are plural but refer to a unified pair of objects, such as (eye)glasses, pants, and scissors, are nevertheless associated with plural verbs: “My glasses are missing”; “These pants have gotten too tight”; “The scissors are dull.”
Words in several other categories are categorical exceptions: Proper names, composition titles, and words used as words are always singular, even if they are plural in form:
Acme and Sons is a highly rated company.
Spats is a downtown bar.
Demons is a terrible movie.
Shades is a best-selling novel.
Hits is an informal word meaning “search returns.”
Aussies is a nickname for Australians.
A few words appear to be plural but are in fact taken directly from other languages in which s at the end of a word does not denote a plural form. For example, biceps (from Latin) is singular, though many people refer to the muscle in the front of one upper arm as a bicep, and kudo (from Greek) is widely employed as the singular form of kudos — meaning “praise” or “prestige” — though the latter form is singular. (Bicep and kudo are back-formations — linguistic innovations of varying legitimacy — but are not advisable in formal writing.)
Rarely, you’ll see a word that is plural in both appearance and usage, though the literal meaning of the word is singular. For example, whereabouts means “location,” but one writes that a person’s whereabouts are unknown (even though a person can be in only one location at once).