The American Heritage® Dictionary of the English Language: Fourth Edition. 2000.
Appendix I
Indo-European Roots
ENTRY:
sker-3
DEFINITION:
Excrement, dung. Oldest form *ser-, becoming *sker- in centum languages. 1. Suffixed unextended form *sk-r, alternating with *sk--. scato-, scoria, skatole, from Greek skr (stem skat- < *sk--t-), dung. 2. Extended form *skert- in taboo metathesis *sterk-os-.a.stercoraceous, from Latin stercus, dung; b. variant forms *(s)terg-,*(s)treg-.dreck, from Middle High German drëc, dung, from Germanic *threkka-. (Pokorny ser-(d-) 947, 8. (s)ter- 1031.)