definition
A magazine or newspaper published at regular intervals; Occurring or appearing at intervals; occasional:
sentence
He has a diploma in journalism and has published several features, stories and poetry in magazines and periodicals
At periodical intervals, the network returns the data to a central control room by cellular phone, satellite, or a conventional telephone circuit.
difficulty
easy
toefl frequency
3
toefl classification
adverb
periodically
adverb sentence
I will periodically check on your progress