fossil fuel

a seed / a pit or stone in a fruit / a gamete (reproductive cell such as a spermatozoan or egg) / a lineage, bloodline / an origin, cause / the materials or ingredients from which something is made

fuel

a fossil / petrifaction / (metaphor, insult) out-of-date person, thing

to fossilize

seed / plant, sow / class, kind, variety / (taxonomy) species

a female given name / a surname

an origin, cause / a type, class

counter for number of kinds or types

an origin, cause / a type, class / an interest, appeal