This is the 365th most frequent Croatian word.
svibnja
"Svibnja" means "May" (the month) in English.
In this sentence, 'svibnja' is used in the genitive case to indicate the date of the month of May after the ordinal number.
Prvi svibnja obilježava Praznik rada.
The first of May marks Labour Day.
Here, 'svibanj' is used in the nominative case as the subject of the sentence, referring directly to the month of May.
Cijeli svibanj je bio sunčan i topao.
The whole May was sunny and warm.
In this usage, 'svibnja' is in the genitive case because it follows the preposition 'sredinom,' which governs genitive.