understandably
adv.used to say that a reaction or feeling is easy to understand or makes sense in a specific situation.
adv.in a manner that is easy to comprehend or justify given the circumstances. Often functions as a disjunct to express the speaker's empathy or logical agreement with a situation.
“She was understandably upset when she lost her keys.”
“The passengers were understandably frustrated after their flight was delayed for the third time in one day.”
“Having invested his life savings into the venture, he was understandably cautious about signing the new contract without a thorough legal review of the fine print.”
Sentence adverb — often placed at the beginning of a sentence or before the main adjective to comment on the entire situation.
Learners often use the adverb form after 'it is' instead of the adjective 'understandable'.
“Understandably, families who have been through this have campaigned relentlessly for local and national investigations.”
“Some business groups are understandably not happy about the decision.”
From understandable + -ly.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.