尺子(chǐ zi) - ruler in Mandarin

尺子 (chǐzi) is the ruler used for drawing straight lines and measuring. 尺 (chǐ) is an old unit of length, roughly a third of a metre, as well as the word for a ruler, and 子 (zi) here is the common noun suffix, said with a light neutral tone rather than a full third tone.

That neutral tone matters: pronouncing the second syllable as a full third tone instead of the neutral one sounds off to a native ear, even though the meaning stays clear from context. The same neutral-子 (zi) pattern shows up in plenty of everyday objects, so it is worth fixing early.

The measure word is 把 (bǎ), used for tools with a handle: 一把尺子 (yì bǎ chǐzi), "one ruler", the same measure word used for 一把伞 (yì bǎ sǎn), "one umbrella".