главня

Inherited from Proto-Slavic *golvьňa:

• Per BER: derived from Bulgarian глава́ (glavá, “head”), гла́вен (gláven, “main, capital”) (see Etymology 3).
• Per Machek, Stankiewicz: probably from an earlier *golv- (“to decay, to languish”) + -ня (-nja), akin to Lithuanian gélti (“to sting”), pagalỹs (“log, stick”), Latvian galēt (“to slay”), gals (“end, demise”).

главня́ or гла́вня • (glavnjá or glávnja) f

1. log of burnt wood, ember

   Synonym: (dialectal) поле́но (poléno)

• гламня́ (glamnjá), гла́мня (glámnja), гла́мна (glámna) — dialectal, with assimilation of -вн- > -мн-

• “гнавня¹”, in Речник на българския език [Dictionary of the Bulgarian Language] (in Bulgarian), Sofia: Bulgarian Academy of Sciences, 2014
• “главня”, in Речник на българския език [Dictionary of the Bulgarian Language] (in Bulgarian), Chitanka, 2010
• Georgiev, Vladimir I., editor (1971), “гламница, гламня”, in Български етимологичен речник [Bulgarian Etymological Dictionary] (in Bulgarian), volumes 1 (А – З), Sofia: Bulgarian Academy of Sciences Pubg. House, →ISBN, page 246

главня (disease)

Likely from the same origin as Etymology 1.

главня́ • (glavnjá) f

1. infectious disease attacking crops
2. smut (fungus that causes the infectious disease)

• “гнавня²”, in Речник на българския език [Dictionary of the Bulgarian Language] (in Bulgarian), Sofia: Bulgarian Academy of Sciences, 2014
• “главня”, in Речник на българския език [Dictionary of the Bulgarian Language] (in Bulgarian), Chitanka, 2010

Probably from глава́ (glavá, “head”) +‎ -ня (-nja), originally meaning head-like, shaped like a head.

главня́ • (glavnjá) f

1. (dialectal) maul (sledgehammer with a large head)

• “главня³”, in Речник на българския език [Dictionary of the Bulgarian Language] (in Bulgarian), Sofia: Bulgarian Academy of Sciences, 2014