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know from a bar of soap

(UK, Australian, NZ, South Africa, idiomatic, informal) To know; to be acquainted with (a person).

219 viewsLast reviewed Jun 29, 2026+ Add a definition
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UK
#1·Apr 27, 2026UK

(UK, Australian, NZ, South Africa, idiomatic, informal) To know; to be acquainted with (a person).

After she won the lottery, Marge had long-lost relatives she didn't know from a bar of soap come up to her to ask for money.
For parents

"know from a bar of soap" means: To know; to be acquainted with (a person).. This is informal slang, common in casual speech, texting and social media, but not appropriate for school work, applications or professional settings. There is no real cause for concern in itself; it is everyday peer vocabulary. If your child uses it, a light comment about audience and register is usually enough — no need to escalate. Context, more than the word, tells you whether to follow up.

For ESL learners

"know from a bar of soap" means: To know; to be acquainted with (a person).. Register: informal slang, fine in casual conversation, texting and social media but not in academic essays, business writing or formal speech. Note the regional or dialect label (UK) — usage may sound odd outside that variety. A common non-native mistake is to use the word in the wrong register, or to assume one fixed meaning when it is actually polysemous; always check the surrounding register and the audience before producing it yourself. In formal writing, prefer a neutral synonym or a short descriptive phrase, and use this word only when you have heard or read it being used naturally in

Cluster: general
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For specific readers

"know from a bar of soap" means: To know; to be acquainted with (a person).. This is informal slang, common in casual speech, texting and social media, but not appropriate for school work, applications or professional settings. There is no real cause for concern in itself; it is everyday peer vocabulary. If your child uses it, a light comment about audience and register is usually enough — no need to escalate. Context, more than the word, tells you whether to follow up.

Why is this section here?

Slang is read by different audiences for very different reasons. The For parents view re-explains the term in plain, non-judgemental language so a caregiver can understand what their child means without needing the surrounding subculture. The For English learners view focuses on register (when it's safe to use), formal alternatives, and common mistakes — what a textbook won't teach you.

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