I always explain this in the introduction to linguistics, and I always explain this again when I talk about term papers in my seminars, and it’s on the PDF on term papers as well, but somehow, people either seem to get confused or don’t find this important, so I’ll address the issue here as well: when to use single quotation marks and when to use italics.

When you are referring to the form of a phrase, word or morpheme, you should use italics. When you want to talk about the meaning of linguistic material, you should use single quotation marks:

1. The Old English word stræte goes back to Latin strata, which means ‘straight (road)’.
2. Beoncé introduced slay in her lyrics, as a synonym for succeed.
3. Beoncé introduced slay in her lyrics, in the sense of ‘succeed’.

Double quotation marks are reserved for direct quotations. Don’t use them for anything else.

Slashes are used for phonemic transcriptions (and brackets for phonetic transcriptions). Angle brackets are used to mark letters. Curly brackets are sometimes used for morphemes, but morphemes can also be put in italics (with a hyphen), when their form is meant:

4. The German infinitive ending {en}, though spelled with an <e>, is usually pronounced [n̩], [ŋ̩] or [m̩].
5. The German infinitive ending -en, though spelled with an <e>, is usually pronounced [n̩], [ŋ̩] or [m̩].