'Log in' vs. 'login' and other one-word-or-two conundrums

A while back someone ask me about “login.” Should it be one word or two, she wanted to know. Or, more precisely, she wanted to know where I “stand” on the matter.

 While I’m always flattered when someone thinks my opinion is worth a diddle, the truth is that it’s not. So “where I stand” is wherever a good style guide or reference book tells me to stand.

According to the Associated Press Stylebook, “login” is a noun and “log in” is a verb. So, if you're following AP style, you use your login to log in. Piece of cake.

The Chicago Manual of Style doesn’t have an entry for "login." And neither Webster’s New World College Dictionary nor Merriam-Webster’s includes a listing for the word. So documents edited in Chicago style should use the two-word "log in" for both the noun and the verb.

 The “login” situation is a good guide for other one-word-vs.-two-word conundrums. Often, the noun form is one word and the verb is two words. Take “lineup”/ “line up”: You tell all the players in the lineup to line up on the field. Most style guides and dictionaries agree on this matter.

Here are some stumpers that are easily solved simply by applying the noun-is-one-word formula:

 makeup / make up – One word as a noun meaning composition or construction: the patient’s psychological makeup. Also one word as a noun meaning cosmetics (though American Heritage also allows “make up.”) Two words when a verb. 

 backup / back up – One word as a noun or adjective referring to an accumulation (The sink overflowed because of all the backup) or a form of support (Chief, call for backup). Two words as a verb.

 workout / work out – One word as a noun, two as a verb.

 pickup / pick up – Whether you're talking about a truck, a UPS man fetching a package you want delivered, or succeeding with a romantic prospect, the noun is one word and the verb two.

 giveaway / give away – One word as a noun, two words as a verb.

signoff / sign off – Ditto above. One word as a noun, two as a verb.

leftover / left over - Ditto that ditto. One word as a noun, two as a verb.

And, by the way, nouns can function as adjectives. So if you have a makeup case, a pickup time, a backup plan, a workout routine, or lineup changes, those are all one word.