Predominantly means for the main part, mostly. Predominantly is the adjective form of the word predominant. It is derived from the Middle French word prédominant.
Predominately means for the main part, mostly. Predominately is the adjective form of the word predominate. It is derived from the Medieval Latin predominatus. Predominantly and predominately are interchangeable, they both mean for the main part, mostly. The Oxford English Dictionary accepts both spellings, as both words date back to the mid-1500s. However, many scholars prefer the word predominantly. The word predominantly is used nearly twenty times as often as the word predominately, according to Google’s Ngram Viewer.
Examples
Nashville’s predominantly white police force adds to distrust felt in minority neighborhoods, some community leaders say. (The Tennessean)
The decision by the UK in June to leave the EU could throw up some complications for Diageo, however, with wrangling already seen between Scotland (whose electorate voted predominantly to remain in the EU) and the rest of the UK over the decision. (The South China Morning Post)
The report records a number of “consistent themes” from interviews with stakeholder groups, identifying a significant decline in water quality (predominantly underwater visibility region-wide since the mid-1970s), and a general perception of increased sedimentation throughout rivers and estuarine systems. (The New Zealand Herald)
“And it’s a, I believe, a predominately African American church, where he feels right at home with other people of faith,’ she continued. (The Daily Mail)
The Paharis’, who are predominately upper caste Muslims, demand for the ST status is based on a claim that their socio-economic condition is similar to the Gujjars. (The Chandigarh Tribune)
With the country’s gaze firmly affixed on its 50th anniversary of independence celebrations, the nation building theme was a recurring one, with costumes, backdrops and props predominately using the national colours of ultramarine, gold and black being used – to a large extent unintentionally blurring the performances because of the similarity in content. (The Barbados Advocate)