薪 is a bound form (b.f.) that typically appears as a morpheme in compound words rather than alone. Historically it meant 'firewood', which later extended to 'fuel' and then 'salary' (since firewood was once a form of payment). Common compounds include 薪水 (salary), 年薪 (annual salary), 月薪 (monthly salary), and 加薪 (to give a raise).