This is the 9040th most frequent Russian word.
ромашка
"Ромашка" means "chamomile."
'Ромашек' is the plural genitive form of 'ромашка', referring to daisies in general.
Я подарил букет ромашек своей сестре.
I gave a bouquet of daisies to my sister.
'Ромашками' is the instrumental plural form of 'ромашка', used here to describe something associated with daisies.
Она сидела на поляне, пахнущей ромашками.
She was sitting in a field filled with the scent of daisies.
'Ромашка' is used here in its singular form to denote one daisy.