原始 (yuán shǐ) means 'primitive, undeveloped' (原始森林) or 'original, first in time' (原始记录). Unlike 原来 (yuán lái), which describes something that was true in the past but has changed ('originally, at first'), 原始 emphasizes the earliest or most basic state, often unchanged. 原 (yuán) is a shorter, more formal form used in compounds (原文件 'original document').