The word "几千" is formed by directly combining the character 几, which denotes an indeterminate small number (like "several" or "a few"), with the character 千, which is the specific numeral for "thousand". This pairing creates a single, fused concept where the vagueness of "几" is applied to the specific scale of "千", resulting in the approximate quantity meaning "several thousand". It is a straightforward numerical approximation built by attaching a prefix of indeterminacy to a fixed unit of measure.