Learn Swedish: Vi måste minska beroendet, inte minst av fossil energi. - We must reduce the dependence, not least on fossil energy.

It translates to "not least" and acts as an emphasizer. It singles out fossil energi as the most critical part of the broader statement about reducing dependence, highlighting it as the most significant example.

Why do we use the preposition av instead of a word meaning "on" for "dependence on"?

In English, we say "dependence on" or "dependent on", but in Swedish, both the noun ett beroende (a dependence or addiction) and the adjective beroende (dependent) take the preposition av (literally "of"). This is a set prepositional combination that is best memorized.

Why is the adjective fossil used here without a -t or -a at the end?

Energi is an en-word (en energi), so the adjective takes the basic form fossil. You might be more used to seeing the plural form fossila because of the very common phrase fossila bränslen (fossil fuels), but here energy is treated as a singular, uncountable concept.

Why is beroendet in the definite form here?

While English sometimes drops the "the" when talking about reducing "dependence" in a general, abstract sense, Swedish prefers the definite form for abstract nouns when they refer to a specific, contextually known societal issue—in this case, our current global energy dependence.